Pretty much anything is possible. Just look at XRumer, it can register for multiple free email accounts, then register on a forum, and it will create a thread conversation with itself, asking questions about a product with one user and answering the questions with another (timed in random waves).
What you are asking of it could almost completely be done with a script (bash could take care of most of it, perl would be ideal). Using a text based web browser or "cat"ing a thread could easily allow a script to scan ("grep") for certain words, either ones stored in a database, in a file, or base it solely on the number of times the word occurs. Polling wikipedia is simple enough too. Even Word comes now with the ability to "summarise" a document by cropping out sentences and giving you a select amount of sentences. So that can be done as well.
Making the bot appear more human-like can get difficult, stock statements could be stored and inserted into posts. As could pictures. The more human interaction would make this easier, but then it cuts down on the usefulness.
AI is advancing at incredible rates though, and within the next few years, we will run into bots-from-Hell. Once it is more mainstream, bots will become more and more autonomous and be able to carry on disturbingly coherent conversations. In fact, they could one day be amongst some of the best posters on a forum.